Rotation actuators having a flat structure have been proposed in Patent Documents 1 and 2. The rotation actuators (motor with reduction gear) described in these documents are composed of a flat outer-rotor-type motor and a flat epicyclic reduction gear disposed adjacent thereto.
In Patent Document 1, a motor rotating shaft and a reduction gear output shaft are coaxially disposed, the motor rotating shaft is supported by a pair of roller bearings, and the reduction gear output shaft is supported by a cylindrical sliding bearing. In Patent Document 2, a sun gear of an epicyclic reduction gear is formed on the external peripheral surface of the leading-end part of a motor rotating shaft. The motor rotating shaft is supported by a pair of ball bearings and the leading-end part positioned on the reduction gear side thereof is supported by a single ball bearing.
In Patent Document 2, a reduction gear carrier, which is a rotation output member, is supported by a gear base and motor base on the fixed side via a plurality of thrust bearings. The thrust applied to the carrier is thereby borne by the fixed-side members.